1. Field of the Invention
The present invention generally relates to a method for manufacturing a cutting blade having a hardened outer rim that is initially formed as a continuous outer rim diffusion bonded to a core which is then cut to produce a segmented blade.
2. Description of the Related Art
Cutting blades have been proposed that have hardened particles embedded in the outer rim to cut extremely hard surfaces, such as concrete, masonry and the like. These saw blades are rim typically formed with a steel core and a continuous or segmented rim embedded with the hardened particles, such as diamonds, tungsten carbide, polycrystalline diamond and the like (hereafter collectively referred to as "diamond particles").
In the past, methods have been proposed for manufacturing diamond blades which were dependent upon the configuration and function of the blade. These blades are separable into two primary types, blades formed with a continuous outer rim and blades formed with a segmented outer rim. Continuous rim blades are used in applications where chipping is critical, but blade speed is not, such as when cutting tile. Segmented rims are used in applications where chipping is not critical, but blade speed is critical, such as when cutting concrete. As the blade speed increases, typically, the operating temperature increases. If heated sufficiently, the outer segments will expand. The segments expand into the notches therebetween.
To construct a continuous rim blade, one method (U.S. Pat. No. 3,369,879) has been proposed in which an annular grinding member is affixed to a copper ring which is affixed to a steel core of the blade. The steel core is centered within a mold, the core's perimeter is coated with solder, the copper ring is pressed onto the core and bonded thereto with the solder. Next, a mixture containing diamond particles is poured into a cavity in the mold surrounding the copper ring. The mold is closed and heat and pressure are applied to the mixture to "hot press" the rim. This combination of heat and pressure forms a rigid grinding rim and secures the outer rim to the copper ring.
Alternative methods have been proposed for bonding the abrasive rim to the central core (U.S. Pat. Nos. 2,189,259; 2,270,209 and Reissue 21,165). In the method of the '259 patent, the core and the outer rim are separately poured into respective central and outer cavities of a mold. These cavities are separately closed and then aligned with one another and heated and compressed to hot press to the outer rim onto the core. In the method of the '209 patent, a steel central core is centered in the mold and the outer rim mixture is poured into a cavity surrounding this steel core. The mixture is hot pressed directly onto the core. In the method of the '165 reissue patent, the abrasive rim is welded or soldered to the central core.
The '879 patent, '209 patent, and '165 reissue patent are incorporated by reference.
As to the second type of blades, previous methods (U.S. Pat. No. 3,590,535) have been proposed to construct segmented outer rims. In the method of the '535 patent, a plurality of diamond bearing outer segments are formed from a mixture of diamond dust, copper powder and tin powder. Each outer segment is separately press molded onto a corresponding steel underlying segment. The steel underlying segments are machined to fit the contour of the core and subsequently welded thereto.
In an alternative method (U.S. Pat. No. 3,048,160) a blade for cutting hard materials is formed by initially molding a plurality of abrasive cutting segments. As originally formed, each segment includes a serrated bottom surface which is welded to the perimeter of the core by heating, and applying radial pressure against an outer surface of, each segment. An alternative method (U.S. Pat. No. 2,818,850) has been proposed in which the cutting segments are hot pressed such that the included diamond dust is concentrated near the outer surface of the cutting segment. Once hot pressed, an inner surface of the cutting segments are ground to provide a curved surface thereon which substantially corresponds to the outer arc of the blade core. Next, each segment is brazed to the disc core.
However, each of the above methods has only met with limited success. As to the latter group of methods, which separately fasten multiple segments to the core, each of these methods require separate and repeated handling of each segment. More specifically, each segment must be separately hot pressed. Next, each segment must be debarred along its outer surface and ground along its inner surface to form a concave surface thereon, the radius of which substantially corresponds to that of the steel core. Then, each segment must be separately bonded to the core.
Further, this latter group of methods experience extreme difficulty in bonding each segment to the steel core. The diamonds within each segment interfere with this bonding process. To overcome this problem, the '535 patent uses an underlying diamond face or backing layer molded to the diamond section and welded to the core. The '160 patent forms a serrated surface on each segment to effect bonding. The '850 patent utilizes a special molding technique to concentrate the diamond segments proximate the rim's outer surface.
The outer rims also create problems during welding steps since the welders are highly sensitive to the copper and diamond particles within the outer rim. When a welding beam contacts a copper particle, it is partially reflected and consequently less effective at heating the region of the abrasive segment surrounding the copper particle. Also, if the temperature of the welding beam is excessive and the beam contacts a diamond particle, the beam causes carbonization of the diamond particle. Ultimately, the carbonized diamond particle detaches from the segment. Diamond particles within the back side of each segment inhibit the radiusing process in which the concave surface on each segment is machined to match the core. To minimize the effects of the diamond particles upon the grinding and welding processes, a bonding or backing material is formed along the back side of the diamond segment. This backing material is easily ground to the desired radius and easily welded to the core.
Further, diamond blades formed by methods within the former group are void of notches within the core. These notches reduce heating of the blade and help clear foreign particles from the cut during operation. Consequently, blades formed by methods within the former group have more limited applications. If overheated, the continuous rims expand and often fail. Heretofore, it has been impossible to construct a segmented diamond blade without separately forming and securing each diamond segment to the core. The need remains in the industry for an improved method for manufacturing segmented diamond blades. The present invention is intended to meet this need, and to overcome drawbacks previously experienced.